1. Field of the Invention
The present invention relates to a voltage generator and, more particularly, to a voltage generator using a voltage level detector. The present invention provides a means for accurately monitoring and correcting changes in a sensed voltage rail.
2. Description of the Prior Art
Devices using a battery as a power source generally include a positive voltage generator that internally generates a voltage higher than the battery voltage. Similarly, a conventional semiconductor memory device also includes a positive voltage generator that generates a voltage having a higher magnitude than an applied voltage and a substrate voltage generator that generates a substrate voltage having a lower magnitude than a ground voltage.
Both the positive voltage generator and the substrate voltage generator include a voltage level detector, an oscillator and a pumping circuit. The voltage level detector senses an output voltage and generates a voltage signal that represents whether a sensed voltage is higher or lower than a desired voltage level. The oscillator generates a pulse signal in response to this voltage signal that causes the pumping circuit to change the output voltage to a desired voltage level. The voltage generator is activated only when the output voltage becomes higher or lower than the desired voltage level.
The voltage generator generates a voltage having a triangular wave-shape of a predetermined amplitude and period and that is a function of the speed of the voltage level detector and a capacitance associated with the pumping circuit. The generated voltage changes according to a combination of the pumping circuit capacitance and a load capacitance.
Also, a voltage detection threshold of the detector can vary with process variations, which in turn can cause significant variations in the output voltage of the voltage generator. As a result, the voltage generator cannot generate a stable output voltage, and as the output voltage rises significantly, the detector will operate at a greatly reduced speed.
To overcome the problems described above, preferred embodiments of the present invention provide a voltage level detector of a voltage generator that can stabilize an output voltage level even though an internal voltage detection threshold level varies. This reduction in the variation range of the output voltage level increases the operating speed of the voltage generator.
In a preferred embodiment of the present invention, a voltage generator comprising a voltage level detector, an oscillator, and voltage booster provides voltage regulation to an on-chip biasing voltage. The voltage level detector further comprises an amplifier element and an accurate analog-to-digital conversion element, the combination of which provides precision control over an output voltage waveshape and thus the response time of the generator.
By employing a first and a second current source in conjunction with a feedback amplifier, a precision voltage theshold can be used to activate a threshold detector which in turn enables a voltage oscillator to provide an appropriate digital pulse signal to the voltage booster. The voltage booster regulates the magnitude of an output voltage which is fed back to the input of the voltage generator. The present invention can be used to create both positive and negative voltage generators.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.